The project is intended to study the implantation of Strep. mutans in the oral cavity of animals and man. Because implantation studies in humans present several difficulties at present, initial investigation has been limited to implantation of various serotypes of Strep. mutans in gnotobiotic rats. Factors under investigation include the effect of simultaneous introduction of multiple serotypes, the effect of different sugar diets, the effect of prior induction of antibodies to Strep. mutans, and the effect of sequential introduction of each serotype on the implantation of Strep. mutans in gnotobiotic rats.